1. Field of the Invention
The invention relates generally to the field of pulse width communications using precision timing. More particularly, the invention relates to the field of pulse width data transfer using timing that is based on a sub-cycle of the clock controlling a digital circuit.
2. Discussion of the Related Art
Prior art modulation and demodulation techniques are known to those skilled in the art of data transfer. For instance, a conventional modulation technique typically includes modulating a carrier signal with a data signal and then transmitting the modulated carrier. At a receiver, the modulated carrier is demodulated, thereby recovering the data signal. The prior art teaches various methods of time, duration (e.g., pulse-width), amplitude, frequency, phase and acousto-optic modulation.
A problem with conventional approaches is that the demand for bandwidth is growing more quickly than the rate at which the speed of conventional modulation techniques can be increased. Increasing the speed of conventional approaches is limited by the rate at which the speed of the underlying hardware can be increased. Maximizing the speed of available hardware is exponentially costly.
In the past, conventional systems have been aggregated in parallel to provide increased bandwidth. However, a disadvantage of parallel aggregation has been relatively high cost. As the bandwidth provided increases, the cost of the parallel system increases roughly linearly. What is needed is an approach that provides increased bandwidth for data transfer in a more cost-effective manner.
Another problem with parallel systems is that the amount of available spectrum is limited. Aggregating conventional systems in parallel consumes spectrum in a roughly linear manner. What is also needed is a solution that provides more bandwidth for data transfer without occupying more spectrum.
In an effort to satisfy the high data rates required by modern communication systems, modulation of two states of an RF carrier or laser beam has been utilized. A previous approach, involves quadrature amplitude modulation/demodulation. For example, FIG. 3 shows a conventional amplitude-phase modulation approach.
FIG. 3 schematically illustrates a typical circuit for quadrature modulation of a carrier by a bit stream, partitioned into two halves, each half segmented and converted into a sequence of amplitude changes that are then used to modulate both phases of an oscillator signal. The system show in FIG. 3 sums an in-phase carrier that has been amplitude modulated (n/2m amplitude changes/second) with a 90° phase shifted carrier that has been amplitude modulated (n/2k amplitude changes/second).
Referring to FIG. 3, a serial bit stream is split by a demux 310 into a first stream that is fed to a first m-bit buffer 320 and a second stream that is feed to a second m-bit buffer 330. A first modulator 340 is coupled to the first m-bit buffer 320 via a first digital to analog converter 350. A second modulator 360 is coupled to the second m-bit buffer 330 via a second digital to analog converter 370. An oscillator 380 is coupled to the first modulator or mixer 340 and to, via a 90° phase shift 390, the second modulator or mixer 360. The output from the first and second modulators 340, 360 is summed and then sent-on for transmission. The resulting signal is then transmitted for reception at a receiver (not shown in FIG. 3).
FIGS. 4A–4G depict waveforms for selected points of the system shown in FIG. 3. FIG. 4A shows a signal at point S3.1 of FIG. 3. FIG. 4B shows a signal at point S3.2 of FIG. 3. FIG. 4C shows a signal at point S3.3 of FIG. 3. FIG. 4D shows a signal at point S3.4 of FIG. 3. FIG. 4E shows a signal at point S3.5 of FIG. 3. FIG. 4F shows a signal at point S3.6 of FIG. 3. FIG. 4G shows a signal at point S3.7 of FIG. 3.
A problem with conventional quadrature amplitude modulation is that it relies on conventional digital-to-analog conversion for the modulation and conventional analog-to-digital conversion for the demodulation. For high-speed applications, these converters are stand-alone modules not residing in the main processing package (chip). This makes timing issues more critical and requires more on- and off-chip communications that involve data reads and writes over a bus that must be managed by an auxiliary controller. Therefore, what is needed is a solution that does not make timing issue more critical or require more on- and off-chip communications.
The problems and needs discussed above apply to radio frequency (RF), laser, acoustic or light carrier or beam. Therefore, what is needed is an inexpensive and efficient method of modulating and demodulating an RF, laser, acoustic or light carrier or beam for commercial high-speed data transmission systems.
Heretofore, the requirements of economy, spectrum efficiency, and circuit design and operation simplicity referred to above have not been fully met. What is needed is a solution that addresses, preferably all of, these requirements.